The present invention relates to dual deck video recording apparatuses (commonly referred to as "VCRs") of the dual deck type, i.e., apparatuses for copying video signals onto a magnetic storage medium that have more than one operative location for magnetic media. It relates more particularly to a dual deck VCR apparatus and method for preventing use of the same to record a video signal having a copy-protect signal.
Various schemes have been developed for preventing the unauthorized copying of a video signal, such as one encoded on magnetic tape in a video cassette. One of the schemes which has been widely accepted is that described and claimed in applicant's U.S. Pat. No. 4,631,603. This scheme, as well as others, capitalizes on the differences between the circuitry in video recorders and that in standard television sets or monitors. In this connection, while it is desired to adversely affect recording, it is not desired to do so in a manner which will prevent an acceptably viewable picture from being displayed by ordinary television sets and monitors. The scheme described in the aforesaid patent accomplishes this result by adding pulse pairs to a video signal in those aspects of the same which define the vertical blanking intervals during video replay, to interfere with the automatic gain control (AGC) circuitry of a video recorder.
So-called "dual deck" VCR arrangements present special potential problems relative to such copy-protect techniques. Such an arrangement has two different decks or locations, one for playback of a video tape and the other for recording a tape. With such an arrangement, a copy of the video signal recorded on a tape or other magnetic media with a carrier signal, can be fed directly from the playback location to the recording mechanism at the other location without the necessity of the video signal being passed through the automatic gain control and other processing circuitry included to condition signals fed from the exterior of the VCR. Such direct internal copying not only circumvents any copy-protect scheme which relies on circuitry through which externally applied signals pass, it also enables high quality copies to be made. That is, a video signal from the playback deck, after amplification, can be applied directly to the recording mechanism, thus bypassing much complex electronic signal processing, including modulation and demodulation processing, which degrades picture and sound quality. Moreover, copying with a dual deck VCR is quite convenient in that no external cabling is necessary.